CPU Scheduling - Multicore

Reading

Silberschatz et al: Chapter 5.5

Multiple-Processor Scheduling

So far, we’ve only dealt with a single processor

CPU scheduling more complex when multiple CPUs are available due to load sharing.

No single best solutions – no great surprise.

Multiple-Processor Scheduling

Asymmetric multiprocessing (master) Here there is one processor that makes the

decisions for Scheduling, I/O processing, system

activitiesOther processor(s) execute only user

code.

This is a simple approach because only one processor accesses the system data structures, so sharing is not an issue with other processors.

Multiple-Processor Scheduling

Symmetric Multiprocessing (SMP)

Here, each processor is self-scheduling.

Share a common ready queue or each processor may have its own private queue of ready processes.

Multiple-Processor Scheduling

Whether there is a common ready queue or private ready queues, we have a scheduler for each processor that examines the ready queue and dispatches the CPU to a specific process for execution.

Clearly, there are sharing issues, here, since each processor may update this common data structure or try to access a specific PCB in a queue …

Most all modern operating systems support SMP including Windows XP, Solaris, Linux, and Mac OS X.

MultiProcessor Scheduling

Challenges Processor affinity Load balancing

Processor Affinity

Processors have a cache What happens to the cache when a

process leaves the running state The contents of cache memory must be

invalidated Why? The next time the process is schedule

it may be scheduled on another processor Try to avoid migration (processor

affinity)

Load Balancing

Keep the workload balanced among all processors

This is especially a problem in SMP systems

Summary Reviewed multicore